In particular, but not exclusively, the invention is related to Device to Device (D2D) and User Equipment Relay (UER) technology operating under Network (NW) control. As will of course be appreciated for D2D scenarios, a D2D UE communicates with another D2D UE while, for UER scenarios, a UE is relayed (to/from the NW) by another UE with relaying function (UER).
In a network environment, two mobile radio communications devices, such as User Equipments (UEs) can be involved in intra-cell or inter-cell D2D communication (or UE to/from UER communication scenarios) and communicating under NetWork (NW) control. Scenarios also arise where only one of the devices is under NW control, and the other is “out-of-coverage”, or indeed one of the devices can be “under coverage” but out of network control. It is appreciated that the environment within which the devices are located evolves all the time, such as due to changes in position, interference from other cells or other users, power, and distance between the D2D devices. Therefore, it can be beneficial for the NW to know when e.g. a change in the D2D communication might be desirable such that the UEs might look to send information to the NW related to their quality of D2D connection state.
The monitoring of link-quality between two D2D devices is known from a variety of prior art documents such as, for example, PTL1. This document discloses a method for facilitating D2D communication in which a variety of signals are sent between the network and the D2D devices so as to trigger one device to transmit a reference signal, and to request a second device to provide a channel quality indication on the basis of the received reference signal which serves as determining, and reporting, D2D channel quality.
However, the volume of signalling arising in relation to such known arrangements, and their general efficiency of operation, is disadvantageously limiting and leads to undesired transmission overheads and inefficient determination and signalling relating to link-quality. The measurements are taken prior to communication and so are based on legacy pilot transmissions (Sounding Reference Signals SRS) and the measurements are used to determine if D2D communication should take place or not.
Also, from various 3GPP discussion documents, proximity based applications and services have been identified of interest for 3GPP work. This has therefore initiated new Work Items (WIs) and the first step is to investigate the features (or Study Items). However there is little definition of network control of any possible direct communication between the UEs, nor has there been any discussion of the gathering and use of link-quality information.
For example, at the December 2012 RAN plenary meeting, it was agreed to start a Study Item (SI) focussing on LTE device-to-device (D2D) proximity services. The RAN guidance was also to focus on evaluation methodology and channel model only in RAN1#72.
Proximity Services (ProSe) were previously investigated as a SI with SA1, and their conclusions on use cases were summarized in TR 22.803.
During 3GPP TSG RAN WG1 Meeting #72 a Summary of Device to Device Proximity Service Session NPL1, and Draft notes for Study on LTE Device to Device Proximity Services was noted. The study started with respect to a document from a previous meeting (3GPP TSG RAN Meeting #58): NPL2.
Also, an extract from NPL2 (Huawei, HiSilicon—“Evaluation requirements for D2D”) notes that: “The Feasibility Study on Proximity-based Services (FS_ProSe, TR 22.803) has identified valuable services that could be provided by the 3GPP system based on UEs being in proximity to each other. The identified areas include Public Safety and non-Public-Safety services that would be of interest to operators and users.
Proximity-based applications and services represent an emerging social-technological trend. The introduction of a Proximity Services (ProSe) capability in LTE would allow the 3GPP industry to serve this developing market, and will, at the same time, serve the urgent needs of several Public Safety communities that are jointly committed to LTE (see NPL3 and NPL4).
ProSe normative specification is also important to enable economy of scale advantages, i.e. that the resulting system can be used for both Public Safety and non-Public-Safety services, where possible.”
Further from NPL5 it was noted that: “D2D ProSe could be realized within or without LTE network coverage, and in both cases the detection signals are used by UEs for D2D proximity direct discovery without position information. As shown in FIG. 1a/1b, UEs transmit beacon for announcing their existing and detect beacons for discovering proximal devices with or without network-assisted.”
And from NPL6 it was noted that: “Device to device communications can either occur within network coverage or outside network coverage. The outside network coverage case is particularly important for several public safety use cases. In-network coverage device to device communications are possible in both commercial and public safety use cases.”